That's the way my '94 Bounder worked too. If I was going to leave the RV unused for more then 3-4 days, I'd disconnect the battery grounds. Replacing batteries is expensive and that will eliminate any phantom draws, like the engine & tranni ECU's memories or even the radio memories, and of course the CO and Propane detectors. Those all bypass the Main & Aux switches. In your case, even the lights are left on, and so is the step.
I always keep an end wrench and pair of gloves in the battery compartment, even in my Journey now since I sold the Bounder...just for disconnecting the grounds. Takes less than a minute.